Discriminator circuit



Nov. 4, 1952 E. H. HUGENHOLTZ DISCRIMINATOR CIRCUIT Filed Dec. 22, 1948 j d px (Hz) INVENTOR.

HZMPDIZEHIMNHFWOZTZ AGHVI Patented Nov. 4, 1952 DISCRIMINATOR CIRCUIT Eduard Herman Hugenholtz, Eindhoven, Netherlands, assignor to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application December 22, 1948, Serial No. 66,807

. In the Netherlands January 14, 1948 6 Claims.

The invention relates to a discriminator circuit-arrangement for producing a direct voltage, the polarity of which varies with the polarity of the frequency or phase difference of two alternating voltages and may be used with particular advantage to produce a control-voltage required to be fed to an amplifying tube operating as a variable reactance and for use in circuit arrangements for automatic frequency correction (A. F. C.).

For A. F. C. purposes it is known (U. S. P. 2,044,749, Fig. l) to feed quadrature components of one of the alternating voltages required to be compared to the anodes of two triodes which operate as mixin tubes and are controlled cophasially by the other alternating voltage. The

beat voltages of difference frequency then produced have a phase shift of 90 but the polarity of this phase difierence varies with the polarity of the frequency difference of the compared alternating voltages. By supplying the beat voltages through transformers to the control-grids of two further triodes which cut off one another clue to a galvanic cross-wise coupling, one or the other of the two latter triodes will be cut off according as one or the other of the beat voltages leads and there is set up between the anodes a direct voltage the polarity of which varies with the polarity of the frequency difference of the compared alternating voltages.

If according to a proposal made in a prior patent application No. 114,302 (U. S. Patent 2,505,- 642), the phase-shifted beat voltages are fed, through a direct-current passing coupling, to cross-wise coupled amplifying tubes, a circuit-arrangement is set up which indicates not only with correct polarity the frequency differences but also phase diiference of the compared alternating voltages. In the two above circuit-arrangements the value of the direct voltage produced is, to a first approximation, invariably the same.

According to the invention, such circuit-arrangements may be materially simplified by crosswise, preferably galvanic coupling the amplifying tubes operating as mixing tubes for the production of beat voltages. The mixing tubes already available in such circuit-arrangements are thus also utilized for converting the phase difference of the beat Voltages or, in the event of synchronism of the compared alternating voltages, the amplitude difference of the beat voltages into a direct voltage, the polarity of which corresponds to the polarity of the phase or amplitude difference of the beat voltages and which may be taken, through a smoothing filter from the output circuit of the mixing stage,

In contradistinction to the known circuit-arrangement referred to above or to that of the prior patent application, the value of the direct voltage produced is now no longer, to a first approximation, independent of the frequency or phase difference of the compared alternating voltages. On the contrary, with increasing frequency difference of the compared alternating voltages up to a value given by the time constant of the mixing tube circuits, it gradually increases to a maximum value and decreases at higher frequency differences. Such a frequency relation is of particular importance for many uses. In A. F. C. circuit-arrangements stable adjustment to the required state of equilibrium is thus enabled without taking particular precautions.

In the case of sufiicient power and amplitude of one of the alternating voltages required to be compared as generally occurs with automatic frequency correction of a local oscillator with respect to the oscillations produced by the local oscillator, a normal direct anode voltage of the mixing tubes may be dispensed with and that one of the alternating voltages required to be compared which has a sufficient amplitude may be utilized instead as the anode voltage for the two mixing tubes.

In order that the invention may be more clearly understood and readily carried into effect, it will now be described more fully with reference to the accompanying drawing, in which Figure 1 shows a particularly simple embodiment ofv the circuit-arrangement according to the invention. Figure 2 shows the value of the direct output voltage as a function of frequency difference.

Referring to the said figures, the alternating voltages f1 and fa required to be compared are fed to input terminals I and 2. The voltage ii is fed in phase as the anode voltage through coupling condensers 3, 4 to the anodes of triode mixing tubes 5, 6, the interconnected cathodes of which are earthed for the input frequencies through a condenser I instead of a galvanic manner. With the use of phase-shifting networks connected in parallel and in opposite senses and comprising resistances 10, II and condensers 8, 9, the voltage 1'2 has derived from it two quadrature components which are fed through grid condensers l2 and I 3 respectively to the controlgrids of the mixing triodes.

The mixing tubes 5, 6 are coupled cross-wise and in a galvanic manner by connecting the control-grid of each of the mixing tubes, through a resistance Hi and [5 respectively to a preferably adjustable tapping point of a resistance I6 and I! respectively connected between anode and cathode of the other mixing tube.

The direct output voltage occurs across the output condenser l8 of a smoothing filter which comprises a series resistance 19 and which is connected to the anode of the mixing tube 6.

As in the circuit-arrangements of the above kind the anodes of the mixing tubes 5, 6 and hence the condensers 3, 4 and the resistances I1, [6 shunting the tubes have produced across them quadrature beat voltages the frequency of which corresponds to the frequency difference of the compared alternating voltages. If, for example, the beat voltage across the tube 5 leads relatively to that across tube 6, the tube 5 over half a period of the beat frequency takes current before tube 6 and, owing to the cross-wise coupling, more current than tube 6, so that, owing to the cross-wise coupling, tube 6 is substantially cut oif. During a part of the next following halfperiod of the beat frequency which is determined by the time constant of the mixing tube circuit, tube 6 continues to be substantially cut off. Set up between the anodes of the mixing tubes and hence across the series combination of the shunt resistances l6, H is a pulsatory direct voltage, the polarity of which varies with the polarity of the phase-difference of the beat voltages and hence with the polarity of the frequency difference of the compared alternating voltages. This pulsatory voltage is operative across the input circuit of the smoothing filter I8, [9 through a resistance 20 connected between the anode of the tube 5 and earth.

As a matter of course, if the compared voltages are in synchronism, the beat frequency is, zero, the polarity of the phase difference of the beat voltages occurring at a beat frequency which differs from zero becoming manifest as the polarity of the amplitude difference of the beat voltages and a direct voltage the polarity of which corresponds to the polarity of the said amplitude difference being produced across the output condenser IB of the smoothing filter. The value of this voltage varies with the value of the phase difference of the (synchronous) compared voltages.

The relationship between beat frequency and time constant of the mixing tube circuits has been pointed out above. As a matter of fact, if during half a period of the beat frequency the charge of, for example, a condenser 3 connected to an anode of tube 5 produced during a preceding half-period cannot leak away for the greater part, the time constant given by condenser 3, resistance i1 and condenser I being primarily responsible for this leaking away, the residual charge will in the next following halfperiod of the beat frequency, prevent any change in polarity of the voltage across the series combination of the resistances l6, H.

To clarify the effect of the time constant, Fig. 2 shows the value of the direct output voltage e as a function of the frequency difference f1j2 of the compared alternating voltages. In this figure, curve it obtains for a greater time constant than curve b. Compared with curve b, the first-mentioned curve a exhibits a steeper slope. The greater the time constant, the smaller are the difference frequenciesof the compared alternating voltages at which the positive or negative maximum value of the output voltage e occurs.

With alternating voltages of about 10 kilocycles required to be synchronized the following values of the resistances and condensers used in the circuit-arrangement were found to be satisfactory:

R1o=R11 10,000 ohms R14=R15 0.5 megohm R1s=R17 0.5 megohm R19=R2o 0.5 megohm C3=C4 10,000 mmf. C-z 20,000 mmf. Cs=C9 1,330 mmf.

C12=C13 10,000 mmf.

C18 0.5 mf.

The galvanic, cross-wise coupling shown in Fig. 1 may be replaced by a capacitative, inductive or mixed coupling, provision having to be made to prevent excessive increase of the time constant of the coupling circuits. In the case, for example, of a capacitative coupling, the extreme flanks of the curves of Fig. 2 become steeper.

A greater conversion conductance of the mixing tubes is obtainable by the use of a normal direct anode voltage but this results in superposure of the desired output voltage and the direct anode voltage across the output condenser. This may be prevented, if desirable, by taking the output voltage from resistances included in the cathode leads of the mixing tubes.

What I claim is:

1. A discriminator circuit arrangement for producing an output voltage having polarity variations about a given value and magnitudes proportional to the wavelength differences between a first wave and a second wave, comprising first and second electron discharge tube systems each having cathode, grid and anode electrodes and each having an input circuit and an output circuit, means to apply said first wave in phase coincidence to a corresponding one of said circuits of each of said discharge tube systems, a phase shifting network coupled to the other of said circuits of each of said discharge tube systems, means to apply said second wave to said phase shifting network thereby to apply said second wave to the other of said circuits of each of said discharge tube systems in phase displaced relationship and to develop at the anodes of said discharge tube systems a third wave having a frequency value equal to the difference in frequency values of said first and second waves, means intercoupling the anode of said first discharge tube system to the grid of said second discharge tube system and the anode of said second discharge tube system to the grid of said first discharge tube system substantially to block one of said discharge tube systems when the other is conducting, and means to derive said output voltage from said output circuits of said first and second discharge tube systems.

2. A discriminator circuit arrangement for producing an output voltage having polarity variations about a given value and magnitudes proportional to the wavelength differences between a first wave and a second wave, comprising first and second electron discharge tube systems each having cathode, grid and anode electrodes and each having an input circuit and an output circuit, means to apply said first wave in phase coincidence to the output circuits of each of said discharge tube systems, a phase shifting network coupled to the input circuits of each of said discharge tube systems, means to apply said second wave to said phase shifting network thereby to apply said second wave to the input circuits of each of said discharge tube systems in phase displaced relationship and to develop at the anodes of said discharge tube systems a third wave having a frequency value equal to the difference in frequency values of said first and second waves, means intercoupling the anode of said first discharge tube system to the grid of said second discharge tube system and the anode of said second discharge tube system to the grid of said first discharge tube system substantially to block one of said discharge tube systems when the other is conducting, and means to derive said output voltage from said output circuits of said first and second discharge tube systems.

3. A discriminator circuit arrangement for producing an output voltage having polarity variations about a given value and magnitudes proportional to the wavelength differences between a first wave and a second wave, comprising first and second electron discharge tube systems each having cathode, grid and anode electrodes and each having an input circuit and an output circuit, means to apply said first wave in phase coincidence to the output circuits of each of said discharge tube systems, a phase shifting network coupled to the input circuits of each of said discharge tube systems, means to apply said second wave to said phase shifting network thereby to apply said second wave to the input circuits of each of said discharge tube systems in phase displaced relationship and to develop at the anodes of said discharge tube systems a third wave having a frequency value equal to the difference in frequency values of said first and second waves, means comprising a first direct current path intercoupling the anode of said first discharge tube system to the grid of said second discharge tube system and a second direct current path intercoupling the anode of said second discharge tube system to the grid of said first discharge tube system substantially to block one of said discharge tube systems when the other is conducting, and means to derive said output voltage from said output circuits of said first and second discharge tube systems.

4. A discriminator circuit arrangement for producing an output voltage having polarity variations about a given value and magnitudes proportional to the wavelength differences between a first wave and a second wave, comprising first and second electron discharge tube systems each having cathode, grid and anode electrodes and each having an input circuit and an output circuit, each of said output circuits comprising a resistive element having a tapping, means to apply said first wave in phase coincidence to the output circuits of each of said discharge tube systems, a phase shifting network coupled to the input circuits of each of said discharge tube systems, means to apply said second wave to said phase shifting network thereby toapply said second wave to the input circuits of. each of said discharge tube systems in phase displaced relationship and to develop at the anodes of said discharge tube systems a third wave having a frequency value equal to the difference in frequency values of said first and second waves, back-coupling means comprising a first resistor intercoupling the grid of said first discharge tube system and the tapping on the resistive element in the output circuit of said second discharge tube system and a second resistor intercoupling the grid of said second discharge tubesystem and the tapping on the resistive element in the output circuit of said first discharge tube system substantially to block one of said discharge tube systems when the other is conducting, and means to derive said output voltage from said output circuits of said first and second discharge tube systems.

5. A discriminator circuit arrangement for producing an output voltage having polarity variations about a given value and magnitudes proportional to the wavelength differences between a first wave and a second wave, comprising first and second electron discharge tubes each having cathode, grid and anode electrodes, a first resistive element having one end thereof connected to the anode of said first tube, a second resistive element interconnecting the other end of said first resistive element and the anode of said second tube, means to interconnect the cathodes of said tubes and the junction of said first and second resistance elements, means to apply said first wave in phase concidence to the anodes of each of said tubes, a phase shifting network coupled to the grids of each of said tubes, means to apply said second wave to said phase shifting network thereby to apply said second wave to the grids of each of said tubes in phase displaced relationship and to develop at the anodes of said tubes a third wave having a frequency value equal to the difi'erence in frequency values of said first and second waves, back-coupling means comprising a third resistive element interconnecting the grid of said first tube to said second resistive element and a fourth resistive element interconnecting the grid of said second tube to said first resistive element substantially to block one of said tubes when the other is conducting, and means comprising a filter to derive said output voltage from said first and second resistive elements.

6. A discriminator circuit arrangement for producing an output voltage having polarity variations about a given value and magnitudes proportional to the wavelength differences between a first wave and a second wave, comprising first and second electron discharge tube systems each having cathode, grid and anode electrodes and each having an input circuit and an output circuit, means to apply said first wave in phase coincidence to a corresponding one of said circuits of each of said discharge tube systems, a phase shifting network coupled to the other of said circuits of each of said discharge tube systems, means to apply said second wave to said phase shifting network thereby to apply said second wave to the other of said circuits of each of said discharge tube systems in phase displaced relationship and to develop at the anodes of said discharge tube systems a third wave having a frequency value equal to the difference in frequency values of said first and second waves, said output circuits each having a time constant smaller than one period of the maximum frequency of said third wave, means intercoupling the anode of said first discharge tube system to the grid of said second discharge tube system and the anode of said second discharge tube system to the grid of said first tube substantially to block one of said discharge tube systems when the other is conducting, and means to derive said output voltage from said output circuits of said first and second discharge tube systems.

EDUARD HERMAN HUGENHOLTZ.

REFERENCES CITED The following references are of record in the file of this patent:

Usselman Oct. 23, 1945 

